Abrupt Decrease in Serum Testosterone Levels After an Oral Glucose Load in Men: Implications for Screening for Hypogonadism
Caronia LM, Dwyer AA, Hayden D, Amati F, Pitteloud N, Hayes FJ. Clin Endocrinol (Oxf). 2012 Jul 17. doi: 10.1111/j.1365-2265.2012.04486.x. [Epub ahead of print]


Reproductive Endocrine Unit of the Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts, 02114.



This study examines the physiological impact of a glucose load on serum testosterone (T) levels in men with varying glucose tolerance (GT).


Cross-sectional study


74 men (19-74 years, mean 51.4 ± 1.4 years) underwent a standard 75g oral glucose tolerance test with blood sampling at 0, 30, 60, 90, and 120 min. Fasting serum glucose, insulin, total T (and calculated free T), LH, SHBG, leptin and cortisol were measured.


57% of the men had normal GT, 30% had impaired GT, and 13% had newly diagnosed type 2 diabetes. Glucose ingestion was associated with a 25% decrease in mean T levels (delta = -4.2 ± 0.3 nmol/L, p <0.0001). T levels remained suppressed at 120 minutes compared to baseline (13.7 ± 0.6 vs. 16.5 ± 0.7 nmol/L, p <0.0001) and did not differ across GT or BMI. Of the 66 men with normal T levels at baseline, 10 (15%) had levels which decreased to the hypogonadal range (<9.7 nmol/L) at one or more time points. SHBG, LH, and cortisol levels were unchanged. Leptin levels decreased from baseline at all time points (p <0.0001).


Glucose ingestion induces a significant reduction in total and free T levels in men, which is similar across the spectrum of glucose tolerance. This decrease in T appears to be due to a direct testicular defect but the absence of compensatory changes in LH suggests an additional central component. Men found to have low non-fasting T levels should be reevaluated in the fasting state.